In automotive mechanics, a gear arrangement that transmits power from the engine to a pair of driving wheels , dividing the force equally between them but permitting them to follow paths of different lengths, as when turning a corner or traversing an uneven road.
On a straight road the wheels rotate at the same speed; when turning a corner the outside wheel has farther to go and would turn faster than the inner wheel if unrestrained. The automobile differential was invented in 1827; originally used on steam-driven vehicles, it was well known when internal-combustion engines finally appeared.